Interaction of mannose-binding protein with associated serine proteases: effects of naturally occurring mutations

• Published in: The Journal of biological chemistry Vol. 275; no. 40; pp. 30962 - 30969
• Main Authors: Wallis, R, Dodd, R B
• Format: Journal Article
• Language: English
• Published: United States 06.10.2000
• Subjects: Amino Acid Sequence; Animals; Binding, Competitive; Calcium - metabolism; Carrier Proteins - metabolism; Collectins; Complement Activation; complement component C1q; complement component C1r; complement component C1s; Complement System Proteins - metabolism; Disulfides; DNA, Complementary - metabolism; Dose-Response Relationship, Drug; Electrophoresis, Polyacrylamide Gel; Glycosylation; Kinetics; Mannose-binding protein; Mannose-binding protein-associated serine protease-1; Mannose-binding protein-associated serine protease-2; Mannose-Binding Protein-Associated Serine Proteases; Molecular Sequence Data; Mutation; Protein Binding; Protein Structure, Tertiary; Rats; Recombinant Proteins - metabolism; Sequence Homology, Amino Acid; Serine Endopeptidases - chemistry; Serine Endopeptidases - genetics; Serine Endopeptidases - metabolism; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
• ISSN: 0021-9258
• DOI: 10.1074/jbc.M004030200

Mannose-binding protein (MBP; mannose-binding lectin) forms part of the innate immune system. By binding directly to carbohydrates on the surfaces of potential microbial pathogens, MBP and MBP-associated serine proteases (MASPs) can replace antibodies and complement components C1q, C1r, and C1s of the classical complement pathway. In order to investigate the mechanisms of MASP activation by MBP, the cDNAs of rat MASP-1 and -2 have been isolated, and portions encompassing the N-terminal CUB and epidermal growth factor-like domains have been expressed and purified. Biophysical characterization of the purified proteins indicates that each truncated MASP is a Ca(2+)-independent homodimer in solution, in which the interacting modules include the N-terminal two domains. Binding studies reveal that both MASPs associate independently with rat MBP in a Ca(2+)-dependent manner through interactions involving the N-terminal three domains. The biophysical properties of the truncated MASPs indicate that the interactions with MBP leading to complement activation differ significantly from those between components C1q, C1r, and C1s of the classical pathway. Analysis of MASP binding by rat MBP containing naturally occurring mutations equivalent to those associated with human immunodeficiency indicates that binding to both truncated MASP-1 and MASP-2 proteins is defective in such mutants.